The present invention relates to a multiple electric conductivity measuring apparatus having a plurality of electric conductivity measuring cells, and more specifically, relates to a multiple electric conductivity measuring apparatus capable of accurately measuring a difference or variation of the electric conductivities between measuring points different in position or time in a treatment system containing a substance to be measured such as an aqueous solution and the like.
Electric conductivity is especially employed as a scale to measure a concentration of ions capable of migrating in an aqueous solution, and an electric conductivity measuring apparatus is used to measure ion concentrations in many kinds of aqueous solutions. An electric conductivity measuring apparatus, generally, determines an increase or a decrease of the ion concentration of an aqueous solution to be measured by measuring the resistance of the aqueous solution existing between an electric conductivity detection electrode and an electric current supply electrode connected to a power source.
As a method for using a conventional electric conductivity measuring apparatus, the electric conductivity measuring apparatus is installed at a predetermined measuring point, or a sample solution is introduced from a predetermined measuring point into the electric conductivity measuring apparatus, and the electric conductivity measured by the apparatus is utilized for observing the condition of an aqueous solution or controlling the water quality thereof and the like in many kinds of fields. In the measurement of electric conductivity by the electric conductivity measuring apparatus, usually, the measurement is conducted after adjusting the measuring range of the electric conductivity measuring apparatus in accordance with a condition of a substance to be measured, a condition of an electrode, a condition of the circumstances at the time of the measurement (for example, an ambient temperature or a condition of noises from surrounding equipment) and the like. Further, in this measurement, a surface condition of the electrode often varies with time since organic substances and the like contained in a substance to be measured onto the electrode of the electric conductivity measuring apparatus. In such a condition, a drift from a desired measuring standard point occurs more or less during the measurement. Therefore, the data of the electric conductivity measured by the electric conductivity measuring apparatus are deemed to be data which are relatively low in reliability as data used for operation management or control, and it is the present situation that the data are considered as secondary data.
Especially, in a case where measurement data of electric conductivity are collected from a plurality of measuring points, and, for example, a progress degree of a treatment of an aqueous solution between the plural measuring points, or a variation of water quality between these measurement points, and further, in a case where a variation of the electric conductivity with time is measured at a substantially identical measuring position, practically it is difficult to measure with a high accuracy, because the measuring range of each apparatus is adjusted, or a drift occurs with time, as described above. Further, when a variation of electric conductivity, or a difference in electric conductivities between a plurality of measuring points is to be measured, in a case where the variation or the difference is much smaller than the absolute value of the electric conductivity which is being measured, since the measuring range is adjusted relative to the relatively great absolute value of the electric conductivity, it is very difficult to distinguish such a micro variation or difference, or, the measured data become low in reliability. In practice, however, there are many requirements to measure such a micro difference or variation between two or a plurality of measuring points different in position or time. If such a micro difference or variation can be measured with a high reliability, a high accuracy and a high sensitivity, it is considered that the use is very broad. However, an electric conductivity measuring apparatus capable of satisfying such requirements has not yet been found.
Accordingly, it is an object of the present invention to provide a multiple electric conductivity measuring apparatus capable of measuring a micro difference or variation of electric conductivity between a plurality of measuring points different in position or time with a high reliability, a high accuracy and a high sensitivity to satisfy the above-described requirements.
To accomplish the above-described object, a multiple electric conductivity measuring apparatus according to the present invention comprises at least two electric conductivity measuring cells each having at least two electrodes brought into contact with a substance to be measured, the electric conductivity measuring cells are so connected electrically that sensing signals themselves from the electric conductivity measuring cells can be treated to be added and/or subtracted.
Namely, in a conventional electric conductivity measuring apparatus, a sensing signal from one electric conductivity measuring cell is amplified by an amplifier and the like, and the amplified signal is rectified into a signal with an appropriate level as an output signal for measuring an electric conductivity, and when a plurality of electric conductivity measuring apparatuses are installed, it has been necessary to adjust a measuring range for each electric conductivity measuring apparatus. In the multiple electric conductivity measuring apparatus according to the present invention, however, within the apparatus itself, an electrical calculation treatment such as addition, subtraction and the like is performed with respect to the sensing signals themselves sent from the respective electric conductivity measuring cells, and the signal after the treatment is amplified as needed, and is output as a difference or variation between the electric conductivities measured at the respective electric conductivity measuring cells. Therefore, the multiple electric conductivity measuring apparatus according to the present invention is basically and distinctly different from the conventional technology in that the conventional electric conductivity measuring apparatuses are merely disposed in plural form and a difference or variation between the data measured by the apparatuses is obtained.
In this multiple electric conductivity measuring apparatus according to the present invention, the above-described at least two electrodes in each electric conductivity measuring cell can be constructed from an electric conductivity detection electrode and an electric current supply electrode. The two-electrode formation itself as the constitution of the electrode is heretofore known. To the electric current supply electrode, for example, an AC current is supplied. In a case where a plurality of electric current supply electrodes are disposed, an amplified or attenuated AC current may be supplied to at least one electric current supply electrode. If an AC current is amplified before being supplied to an electric current supply electrode, it can create substantially the same condition that the supplied electric current is multiplied by a predetermined magnification, and the same effect of the multiplication can be obtained also on sensing signals sent from the electric conductivity measuring cells. If an AC current is attenuated before being supplied to an electric current supply electrode, it can create substantially the same condition that the supplied electric current is divided by a predetermined rate, and the same effect of the division can be obtained also on sensing signals sent from the electric conductivity measuring cells. If the sensing signals themselves thus created are added or subtracted, the multiplication or the division is included in the addition or the subtraction, and, when the sensing signals themselves are treated, as needed, it also becomes possible that addition, subtraction, multiplication and division are combined arbitrarily. The signal created after treating the sensing signals themselves sent from the electric conductivity measuring cells as described above can be amplified in order to optimize the level of the output signal, as needed, and in such a case, because an object is the single signal after the treatment, a single amplifier may be provided.
Further, in the multiple electric conductivity measuring apparatus according to the present invention, it may be constituted that each of the electric conductivity measuring cells has three electrodes, the three electrodes include an electric conductivity detection electrode and two AC current supply electrodes disposed on both sides of the electric conductivity detection electrode at respective distances, and an AC current of the same phase is applied to the two AC current supply electrodes. Alternatively, it may be constituted that each of the electric conductivity measuring cells has three electrodes, the three electrodes include an electric conductivity detection electrode, an AC current supply electrode disposed on one side of the electric conductivity detection electrode at a distance, and a grounded electrode disposed on the other side of the electric conductivity detection electrode at a distance. By such three-electrode constitutions, a high-accuracy measurement, free from adverse effects from circumstances such as noises, becomes possible, as described later.
Further, in the multiple electric conductivity measuring apparatus according to the present invention, it is preferred that the above-described at least two electrodes in each electric conductivity measuring cell are constructed so that their electrode surfaces are formed by titanium oxide layers on surfaces of electrode bodies made of a conductive metal. In such a constitution, when organic substances and the like are contained in a substance to be measured, the property for decomposing organic substances based on the photocatalytic activity of the titanium oxide, and its super-hydrophilicity can be effectively utilized, in order to eliminate adverse effects on the measurement of the electric conductivity due to the adhesion or adsorption of the organic substances to the electrode surfaces. It is preferred that light irradiating means is disposed against the titanium oxide layers to provide a photocatalytic activity to the titanium oxide layers. For example, each electric conductivity measuring cell can be constructed so as to have a space for storing a substance to be measured defined between respective electrode surfaces of the above-described at least two electrodes, and light irradiating means that irradiates light onto the respective electrode surfaces.
In this multiple electric conductivity measuring apparatus, it is preferred that light irradiated by the above-described light irradiating means has a wavelength which brings about a photocatalytic activity of the above-described titanium oxide layers. For example, light with a wavelength from about 300 to about 400 nm can be employed. As the light irradiating means, a light source composed of means for irradiating ultraviolet rays and the like such as a black light may be directly employed, and a light guiding material (for example, an optical fiber, or tube and the like comprising a light guiding raw material) to guide light from a light source provided as means for irradiating light may also be employed. Further, the light from a light guiding material may be added to light irradiated directly from a light source.
Further, the above-described space for storing a substance to be measured may be defined by a light transmitting material, and it may be constituted so that the light from the light irradiating means is irradiated onto an electrode surface through the light transmitting material (for example, glass). In this case, if a titanium oxide coating layer capable of transmitting light is provided on the surface of the light transmitting material at its side facing the space for storing a substance to be measured (a surface in contact with solution), adhesion of organic substances and the like to this surface of the light transmitting material can be prevented by super-hydrophilicity and organics decomposition property ascribed to the titanium oxide layer.
Further, the above-described electrode can be produced by, for example, the following method. Namely, a method can be employed wherein an electrode surface is formed by providing on a titanium oxide layer on a surface of an electrode body made of a conductive metal by a surface treatment such as sputtering, plating or the like. Alternatively, a method can also be employed wherein an electrode surface made of a titanium oxide layer is formed by providing oxygen to a surface of an electrode body made of titanium. As the method for forming a titanium oxide layer by providing oxygen, a method based on air oxidation other than a method utilizing electrolysis can be employed.
In the multiple electric conductivity measuring apparatus according to the present invention as described above, a treatment of at least either addition or subtraction is added to the sensing signals themselves sent from the respective electric conductivity measuring cells in the apparatus, and the signal created after the treatment is output as a single sensing signal. A treatment such as amplification and the like is added to this sensing signal, as needed. The sensing signal thus output corresponds to a difference between the detected electric conductivities at positions set with the respective electric conductivity measuring cells, or a variation between the detected electric conductivities at positions set with the respective electric conductivity measuring cells. It is possible that both of the detected electric conductivities are measured at a substantially same condition or same measuring range, it is not necessary to adjust this condition or measuring range to be met with the scale of the absolute value of the electric conductivity, and it may be adjusted depending on the scale of the above-described difference or variation. Therefore, even when the above-described difference or variation is fine relatively to the scale of the absolute value of the electric conductivity, the micro difference or variation can be extracted with a high accuracy and a high sensitivity. Besides, as described above, since the sensing signals themselves from the respective electric conductivity measuring cells when electrically calculating the difference or variation are signals extracted at a substantially same adjustment condition within a single apparatus, a difference in effect due to the adjustment of the measuring range and the like is not generated between the sensing signals themselves from the respective electric conductivity measuring cells which are the sources of the calculation. Therefore, also from this point of view, it is guaranteed that the above-described difference or variation is extracted accurately, and it can ensure very highly reliable data.
Thus, in the multiple electric conductivity measuring apparatus according to the present invention, since sensing signals themselves from the respective electric conductivity measuring cells can be treated to be at least added and/or subtracted, the measuring apparatus can measure a micro difference or variation of the electric conductivity between a plurality of measuring points different in position or time with a high accuracy and a high sensitivity, and an extremely high-reliability data can be obtained with respect to the measurement of electric conductivity.